tests/check/elements/matroskamux.c: Collectpads in core got changed and now also holds a reference to any pad that is...

Original commit message from CVS:
* tests/check/elements/matroskamux.c: (setup_src_pad):
Collectpads in core got changed and now also holds a
reference to any pad that is part of it. Fix refcount
checks in test case accordingly.